lib/preexec: consolidate helper functions

Define the helper functions for `bash-preexec.sh` immediately after importing it, rather than in `lib/theme`.
- `__check_precmd_conflict()` and `save_append_prompt_command()` are generally useful and not theme-specific.
- Add matching `__check_preexec_conflict()` and `safe_append_preexec()`.

themes/base.theme.bash

@@ -583,44 +583,6 @@ function aws_profile {
 	fi
 }
 
-function __check_precmd_conflict() {
-	local f
-	for f in "${precmd_functions[@]}"; do
-		if [[ "${f}" == "${1}" ]]; then
-			return 0
-		fi
-	done
-	return 1
-}
-
-function safe_append_prompt_command {
-	local prompt_re
-
-	if [ "${__bp_imported:-missing}" == "defined" ]; then
-		# We are using bash-preexec
-		if ! __check_precmd_conflict "${1}"; then
-			precmd_functions+=("${1}")
-		fi
-	else
-		# Set OS dependent exact match regular expression
-		if [[ ${OSTYPE} == darwin* ]]; then
-			# macOS
-			prompt_re="[[:<:]]${1}[[:>:]]"
-		else
-			# Linux, FreeBSD, etc.
-			prompt_re="\<${1}\>"
-		fi
-
-		if [[ ${PROMPT_COMMAND[*]:-} =~ ${prompt_re} ]]; then
-			return
-		elif [[ -z ${PROMPT_COMMAND} ]]; then
-			PROMPT_COMMAND="${1}"
-		else
-			PROMPT_COMMAND="${1};${PROMPT_COMMAND}"
-		fi
-	fi
-}
-
 function _save-and-reload-history() {
 	local autosave=${1:-0}
 	[[ $autosave -eq 1 ]] && history -a && history -c && history -r